The invention generally relates to a process for continuously monitoring and controlling various fastener coating processes, which may include but are not limited to processes involving loading and handling of bulk parts, vibratory sorting, heating, coating (powder or liquid) application to fasteners, tumbling, material recycling and curing (xe2x80x9cfastener coating machines and processesxe2x80x9d).
A variety of fastener coating machines and processes are known for handling threaded fasteners (e.g., nuts and bolts) and non-threaded fasteners (e.g., rivets), and for coating them with a polymeric resin for various purposes, as disclosed in the following U.S. Patents, each of which is assigned to the present assignee and each of which is incorporated by reference herein: U.S. Pat. Nos. 4,060,868; 4,120,993; 4,801,043; 4,888,214; Re. 33,766; 5,236,505; 5,362,327; 5,403,624; 5,620,741; 5,685,680; 5,718,945; 5,758,798; 5,792,512; 5,908,155; 6,004,627; 6,017,391; 6,156,392; 6,168,662 B1; 6,209,758 B1; and 6,223,953 B1.
While these fastener coating machines and processes have proven useful, a fairly high degree of operator control has been required. It would be advantageous, therefore, to automate the processes, rendering them materially faster and more efficient, while also substantially enhancing quality control. Doing so requires resolution of various problems, and combining various designs and technologies, as discussed below.
To provide a few examples, various subsystems must be ready and properly operating for use with a typical fastener coating machine. Such subsystems include those supplying electricity, compressed air, and process heat to a machine. Subsystems for supplying the fasteners and also for supplying the coating material must also be available, e.g., filled reservoirs, free and unblocked feed tubes, etc. Heating coils, for example, must be powered, conveyors or turntables on dial machines must be powered and moving, and vacuum pressure must be available for coating reclamation. If one or more of these subsystems fail, attempted fastener processing can result in defective and unusable parts or damaged machinery. As an example, if a machine conveyor stalls for some reason, such as a defective motor, continuous heating of parts positioned within the induction heating coil will result in a fire, and destroy the induction heating track.
As another example, when a fastener processing machine first begins to run, the fasteners may not have time to reach the specified target temperature before entering the powder application zone. Since such fasteners, called xe2x80x9cpurgedxe2x80x9d fasteners, may not receive a properly adhering coating, it would be advantageous to purge these fasteners from the process before any coatings are applied.
Also, temperature control is critical to obtaining a proper coating, but its regulation and maintenance may be limited to an operator""s subjective view of the xe2x80x9ccolor changexe2x80x9d in the fasteners. As another example, the continuous availability of compressed air (as opposed to its use only when needed) with various fastener machines, disclosed in the patents recited above, increases utility costs and noise levels.
As a further example, coated fasteners must be inspected for quality control. Manual inspection requires the presence of an operator, limits processing speed, and is also dependent on variable parameters such as operator fatigue.
As a still further example, coating reclamation (e.g., using vacuum procedures to reclaim oversprayed coating material), particularly if done manually, may also interrupt fastener processing.
Each of these problems may be minimized or eliminated using automated processing provided by the present invention, as described below.
One aspect of the present invention incorporates the use of a machine vision system. Machine vision systems are known for monitoring and controlling various processes. See, e.g., U.S. Pat. Nos. 6,114,705; 6,172,748 B1; 6,175,652 B1; 6,170,973 B1; and 6,208,772 B1, each of which is incorporated by reference herein. A machine vision system typically provides automated, computer-based image acquisition and analysis capabilities, that can be employed for tasks such as measurement and inspection of fastener components or materials. A machine vision system employs a camera for acquiring an image of an object, and functionality for processing the acquired image and providing desired information about the fasteners as they are coated.
Accordingly, it is an object of the present invention to provide an automated system for processing the coating of fasteners.
It is another object of the invention to provide such a system which is capable of being retrofitted onto existing fastener processing machines.
It is another object to provide processing controls, including a processing controller incorporating the use of a programmable logic controller and a machine vision system, designed and configured to automatically and remotely control the processing of various types of fastener processing machines.
Definition of Claim Terms
The following terms are used in the claims of the patent as filed and are intended to have their broadest meaning consistent with the requirements of law. Where alternative meanings are possible, the broadest meaning is intended. All words used in the claims are intended to be used in the normal, customary usage of grammar and the English language.
xe2x80x9cFastenerxe2x80x9d means threaded parts (e.g., nuts and bolts) as well as non-threaded parts (e.g., rivets) coated with a polymeric resin in either liquid or powder form, using the invention.
xe2x80x9cFastener conditionsxe2x80x9d means predetermined condition(s) to be monitored by the process controller of the present invention, such as but not limited to the number of threads on the fasteners, the orientation of the threads on the fasteners, or the orientation of the fasteners.
xe2x80x9cMachine vision systemxe2x80x9d means a system which acquires an image and processes that image in order to evaluate predetermined variables, parameters or criteria with regard to fasteners being processed using the invention.
xe2x80x9cPredetermined criteriaxe2x80x9d means predetermined parameters or variables to be monitored by the process controller of the invention concerning fasteners to be properly processed, including fastener conditions as well as other conditions, such as the amount of coating coverage on the fasteners, the location of coating on the fasteners, etc.
xe2x80x9cRejected fastenersxe2x80x9d means fasteners which do not meet the predetermined process criteria necessary for qualifying a processed fastener as a xe2x80x9cgoodxe2x80x9d part (e.g., appropriate number of threads, appropriate coating coverage).
xe2x80x9cPurged fastenersxe2x80x9d means fasteners which are purged, or removed, from the production process during machine startup and shutdown cycles. Purged fasteners may (or may not) have been previously heated. However, purged fasteners have never been subjected to application of a coating and, therefore, may be recycled by the processing equipment.
xe2x80x9cGood fastenersxe2x80x9d means fasteners which meet the predetermined process criteria.
The objects mentioned above, as well as other objects, are solved by the present invention, which overcomes disadvantages of prior art process controllers, while providing new advantages not previously obtainable.
In a preferred embodiment, a process controller is provided for monitoring and controlling processing steps involving the application of polymeric resin coatings onto fasteners using processing steps based on predetermined criteria. The fasteners may move or be moved along a pathway located on, or adjacent to, a coating work station. During processing, the process controller automatically performs each of the following mentioned steps. First, an initiation sequence may be performed which confirms the availability of one or more subsystems supplying one or more of the following preconditions: compressed air, heat for use in coating the fasteners, vacuum pressure for a powder coating reclamation system, and presence of sufficient coating material. The heat for use in coating the fasteners may be provided by an induction coil, infrared rays or other heating mechanisms such as those providing conductive heat. The process controller may, but need not, selectively control the presence of compressed air using an air solenoid.
After confirming the availability of one or more of the preconditions, control signals may be initiated to actuate one or more of the subsystems supplying one or more of the preconditions. During fastener processing, one or more of the following run conditions may be continuously monitored for a negative run condition, which may result in the processing of fasteners not meeting the predetermined criteria: fastener speed along the pathway within a predetermined range, coating flow, and heating within a predetermined temperature range. Temperature sensing may, but need not, be accomplished using an optical pyrometer. Also during fastener processing, one or more of the following preselected fastener conditions may be continuously monitored for a defective fastener condition using a machine vision system in communication with the process controller: the number of threads on the fastener, the location of threads on the fastener, the orientation or pitch of the threads on the fastener, the amount of coating coverage on the fastener, and the location of coating on the fastener. Upon detecting a negative run condition, processing may be automatically stopped and the cause of the negative run condition may be indicated. Upon detecting a defective fastener condition, processing may be continued and the detected fastener may be directed to a preselected location for defective fasteners.
In a particularly preferred embodiment, the machine vision system may include a camera and a light source, which may but need not include a fiber optic cable and a halogen bulb. Preferably, the light source illuminates the particular fastener with an illumination power substantially greater than illumination provided by ambient light surrounding the particular fastener. Preferably, the light source provides a substantially constant illumination power over the useful life of the light source.
In one embodiment, the movable pathway is a turntable on a dial machine. Preferably, the turntable is rotated and its speed regulated by a closed loop control system. The closed loop control system may include a motor, a tachometer, and an electronic motor drive. In another embodiment, the pathway may be a belt conveyor.
If the coating material is a liquid, its presence within a delivery tube may be sensed using one or more electronic optical, pressure, or flow sensors. If the coating material is a powder, its presence may be sensed using a capacitive sensor and/or a triboelectric flow monitor.
Preferably, the process controller directs fasteners to be separated into at least three locations: a first location comprising Purged fasteners which have not been coated and which may be recycled for processing; a second location comprising Rejected fasteners which have been found to have a defective fastener condition; and a third location comprising Good fasteners that have been properly processed and meet the predetermined criteria.
Preferably, the process controller provides a visual and/or audible signal indicating the presence of at least one of the following conditions: (1) a major system fault resulting in ceasing of processing; (2) a minor system fault allowing continued processing; and (3) normal processing conditions.